GUIDRV_Lin
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emWin driver GUIDRV_Lin
This driver supports all display controllers with linear video memory accessible via direct interface. It can be used with and without a display controller. The driver does only manage the contents of the video memory. It does not send any commands to the display controller or assumes any specific registers. So it is independent of the register interface of the display controller and can be used for managing each linear mapped video memory.
Supported hardware
Controllers
The driver supports all systems with linear mapped video memory.
Bits per pixel
Supported color depths are 1, 2, 4, 8, 16, 24 and 32 bits per pixel.
Interfaces
The driver supports a direct bus interface from the CPU to the video memory. The video memory needs to be accessible 8, 16 and 32 bit wise.
Color depth and display orientation
The driver consists of several files. They are named GUIDRV_Lin_[O]_BPP.c. where the optional ’O’ stands for the desired display orientation and ’BPP’ for the the color depth. The following table shows the driver files and the configuration macros which should be used to create and link the driver during the initialization:
| Identifier | Color depth and orientation |
|---|---|
| GUIDRV_LIN_1 | 1bpp, default orientation |
| GUIDRV_LIN_2 | 2bpp, default orientation |
| GUIDRV_LIN_4 | 4bpp, default orientation |
| GUIDRV_LIN_8 | 8bpp, default orientation |
| GUIDRV_LIN_16 | 16bpp, default orientation |
| GUIDRV_LIN_OX_16 | 16bpp, X axis mirrored |
| GUIDRV_LIN_OY_16 | 16bpp, Y axis mirrored |
| GUIDRV_LIN_OS_16 | 16bpp, X and Y swapped |
| GUIDRV_LIN_OSX_16 | 16bpp, X axis mirrored, X and Y swapped |
| GUIDRV_LIN_OSY_16 | 16bpp, Y axis mirrored, X and Y swapped |
| GUIDRV_LIN_24 | 24bpp, default orientation |
| GUIDRV_LIN_OX_24 | 24bpp, X axis mirrored |
| GUIDRV_LIN_OY_24 | 24bpp, Y axis mirrored |
| GUIDRV_LIN_OS_24 | 24bpp, X and Y swapped |
| GUIDRV_LIN_OSX_24 | 24bpp, X axis mirrored, X and Y swapped |
| GUIDRV_LIN_OSY_24 | 24bpp, Y axis mirrored, X and Y swapped |
| GUIDRV_LIN_32 | 32bpp, default orientation |
| GUIDRV_LIN_OX_32 | 32bpp, X axis mirrored |
| GUIDRV_LIN_OY_32 | 32bpp, Y axis mirrored |
| GUIDRV_LIN_OS_32 | 32bpp, X and Y swapped |
| GUIDRV_LIN_OSX_32 | 32bpp, X axis mirrored, X and Y swapped |
| GUIDRV_LIN_OSY_32 | 32bpp, Y axis mirrored, X and Y swapped |
The table above shows identifiers which can be used to select the driver. Each combination of orientation and color depth is possible. Please note that currently not all combinations are shipped with the driver. If the required combination is not available, please send a request to obtain the required combination.
Driver selection
To use GUIDRV_Lin for the given display, the following command can be used e.g.:
GUI_DEVICE_CreateAndLink(GUIDRV_LIN_OX_16, GUICC_565, 0, 0);
Please refer to the emWin documentation to get more information about using the proper palette mode.
Display data RAM organization
The picture above shows the relation between the display memory and the pixels of the LCD in terms of the color depth and the endian mode.
Little endian video mode
Least significant bits are used and output first. The least significant bits are for the first (left-most) pixel.
Big endian video mode
Most significant bits are used and output first. The most significant bits are for the first (left-most) pixel.
RAM requirements of the driver
None.
Available configuration macros (compile time configuration)
The following table lists the macros which must be defined for hardware access:
| Macro | Description |
|---|---|
| LCD_ENDIAN_BIG | Should be set to 1 for big endian mode, 0 (default) for little endian mode. |
Available configuraion routines (run-time configuration)
The following table lists the available run-time configuration routines:
| Routine | Description |
|---|---|
| LCD_SetSizeEx() | Changes the size of the visible area. |
| LCD_SetVRAMAddrEx() | Changes the video RAM start address. |
| LCD_SetVSizeEx() | Changes the size of the virtual display area. |
Configuration example
The following shows how to create a display driver device with this driver and how to configure it:
void LCD_X_Config(void) {
//
// Set display driver and color conversion
//
GUI_DEVICE_CreateAndLink(GUIDRV_LIN_8, // Display driver
GUICC_8666, // Color conversion
0, 0);
//
// Display driver configuration
//
LCD_SetSizeEx (0, 320, 240); // Physical display size in pixels
LCD_SetVSizeEx (0, 320, 480); // Virtual display size in pixels
LCD_SetVRAMAddrEx(0, (void *)0x20000000); // Video RAM start address
}
Using the Lin driver in systems with cache memory
The rules to follow are quite simple:
Rule 1
All caches (if applicable, as in your case) should be fully enabled. This means I- and D- caches in systems with separate caches.
Rule 2
All Code and data should be placed in cacheable areas to achieve maximum performance. If other parts of the application require some or all data to be placed in non-cacheable areas, this is not a problem but may degrade performance.
Rule 3
The cache settings for the frame buffer memory (which is really a shared memory area, accessed by both the CPU and the LCD-controller DMA) should make sure, that write operations are ’write-through’ operations. The physical memory should be always up to date, so that the DMA-access of the LCD-controller always get the current content of the frame buffer. In case of a ’write-back’ cache a write operation only changes the content of the cache, which is written to the physical memory not before the cache location is superseded.
In many systems with MMU, this can be achieved by mapping the RAM twice into the virtual address space: At its normal address, the RAM is cacheable and bufferable, at the second address, it is cacheable but not bufferable. The address of the VRAM given to the driver should be the non bufferable address.
If the CPU does not support a ’write-through’ cache the frame buffer memory needs to be uncached.
